Tape extrusion



July 8, 1952 L. F. SAQMLER 2,602,187

TAPE EXTRUSION Original Filed March 11., 1946 2 SHEETSSHEET 1 IN VENTOR.

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' YMM/JM y 1952 L. F. SAMLER 2,602,187

TAPE EXTRUSION Original Filed March 11, 1946 2 SHEETSSHEET 2 m mQ JM,

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Patented July 8, 1952 TAPE izxrnusion Lee F. Samler, Baltimore, Md,assignor to The National Plastic. Products Company, Odenton,

Md., a corporation of Maryland Original application March 11, 1946,Serial No.

653,551. Divided and this application December' 19, 1949, Serial No.133,894

This invention relates to apparatus for the production of extrudedthermoplastic tape and more particularly to the production of such tapeby the utilization of extrusion equipment which will serve to insureuniform cross-sectional thickness and which will maintain the physicaland electrical properties of the thermoplastic.

This application is a division ofco-pending application Serial No.653,551, filed March 11, 1946, which issued on March '7, 1950, as PatentNo. 2,499,421.

Prior to the instant invention, thermoplastic tapes have been extrudedin the conventional manner through a die and onto a moving belt.

1 In practice, when the thickness of thetapeis in excess of .025" it hasbeen found that it is difiicult to control the fiow conditions in thedie and if the exit velocities across the die are not accuratelycontrolled inherent stresses will be set up within the material whichwill ultimately be reflected by distortion and/or shrinkage in thefinished product.- w

It is an object of the instant invention to provide apparatus for theproduction of continuous lengths of substantially stress-freethermoplastic tape oi substantially uniform cross-sectional thickness.

It is another object to provide a novel die assembly for a thermoplasticextruder.

Other objects and the nature and advantages of the instant inventionwill be apparent from the following description taken in conjunctionwith the accompanying drawings, wherein:

Fig. 1 is a schematic view in perspective of an apparatus for carryingout the invention;

Fig. 2 is a schematic view in side elevation of the apparatus shown inFigure 1;

Fig. 3 is a front elevation with parts broken away and parts shown insectionof an extruder die useful in carrying out the invention;

Fig. 4 isa vertical sectional view taken along line 4 -4 of Fig. 3 andlooking in the direction of the arrows; and v Fig. 5 is a bottom view ofthe die shown in Figure 3. s I

Referring to Figures 1 and 2, the thermoplastic compound in eitherpowder, pellet, or other convenient form is introduced into the 'top ofthe feed hopper l0 which is associated with the extrusion cylinder Hwithin which is located the extrusion screw 12. The extrusion .cylinderH may be heated in the conventional manner and in the drawings theextrusion cylinder II is jacketed so that'the cylinder may be heated bysteam, and the pipes 13 and M are part of the 14. Claims. (01. 1s--12)steam heating system for heating the cylinder 1 I. The extrusion screw12 forces the melted plastic compound through the conduit l5 whichconfines the melted plastictoa path which changes the direction offlowfrom that which is coaxial with the axis of the screw to a directionwhich is at right angles to the axis of the screw and in the samehorizontal plane. The conduit i5 is connected at its outlet end it withthe die assembly il. g

The plastic compound in the form of tape leaves the bottom [8 of the dieassembly I1 and in a direction which is aligned with the land of the dieand passes under the roller 19 and moves on toward a position under theroller 2i]. and then upwardly and forwardly to a positionwhere it passesover the guide roll 2! and then horizontally andbetween the washingheaders ZZfrom whence the tape passes between the take-.ofi or pullingrolls 23 which turn in opposite directions in the direction of'thearrows. The tape then passes under the guide roll 24 and is then woundup in the form of a coil 25 on the spindle 29 .of

the reel 21.

The rollers l9 and 2B are journalled for rotation within the tank 28which may contain a tempering liquid. such as water 29, which ternliquidby controlling the flow of steam, through the steam coils 39. Thelocation of the roll 29 may be lowerthan the location of the roll 19 sothat the portion of the tape between the exit of the die and the roll 19will makean angle of more than with a portion of the tape between theroll I9 and the roll 20.

The headers 22 are provided with a series of orificesalong the surfacesadjacent the top and bottom of the extruded tape, which passes betweenthe headers 22 sothat as Washing fluid, which is fed to the manifold 32,passes through the headers 22 it will be directed through said orificesand on to the top and bottom surfaces of the extruded tape which passesbetween the headers 22 to wash same and remove any foreign particleswhich may be picked up in the tempering bath or from the atmosphere. Ex-

prevent the entrance of any foreign the extrusion cylinder ll. The dieI! may be heated by the electric orrice 3. heater 33 which is servedwith electric current by the electric conduits 34 and 35.

Referring to Figures 3, 4 and 5, the die I! may be made of steel and ofthree parts comprisin an inlet adaptor 36, and two major block-likeelements 3! and 38, respectively. The adaptor 36 is formed with atapered opening 39 extending therethrough which is adapted to beassociated with the outlet end l6 of the conduit 15. A tubular manifold40- of relatively large diameter is formed within the die by block-likeelements 31 and 38, and the inlet portion 4| thereof is adapted to beassociated with the passage 39 extend-' ing through the adaptor 36. Themanifold 40 is adapted to extend horizontally and when in position hasits axis at right angles to the axis of the screw 12. As best shown inFig. 5, the narrow sides 43 and 44 and the face 46 of die land 42 areformed in block 37, wherein the inner surface of block 38 forms the face45 of die land 42. The manifold 40 is formed in both blocks 37 and 38 asshown in Fig. 4.

One of the significant elements cooperating in the production of astress-free thermoplastic tape of uniform cross section is the length ofthe effective die land which, in the case of the die ll. is the verticaldistance from the tubular manifold 40 to the bottom 41. This effectivelength of the die land should be at least twenty-five times thethickness of the tape to be produced, and in the production ofpolyethylene tape fifty times the thickness of the tape has been foundto be preferred. In the production of thermoplastic tapes, shorter dielands serve to produce a non-uniform exit velocity across the width ofthe die; that is from the'narrow side 43 to the narrow side 44 at thebottom 41 and a tape produced through the use of such a die has inherentstresses therein. If the axis of the die were in line with the axis ofthe extruder screw, the tendency of the plastic material leaving the dieis to have a greater velocity in the center; that is, midway between thenarrow sides 43 and 44, and a lesser velocity adjacent the narrow sides43 and 44. However, in the case of thick cross sections, such as tapesof a thickness of .02-5" or greater, even with the axis of the die atright angles to the axis of the screw, and even with the die arranged asshown in the drawings, unless the length ofthe effective land of the dieis as described, the exit velocity of the material being extruded willbe greater along the side 43 than along the side 44 so that the sectionof material passing through the die would be generally wedge-shapedinstead of rectangular in shape.

The long land described insures the proper crosssectional shape of thetape.

In the production of polyethylene tape, the exposure of the material tohigh temperatures over a period of time requires critical control ifelectrical properties thereof are not to be degraded Though flowconditions of the material through the apparatus may be improved byincreasing the temperature of the material at the die and in thecylinder, the electrical properties naturally inherent in the materialwill be degraded as it is subjected to high temperatures over a periodof time. The extrusion process inherently requires a given period oftime in its operation and, ac-

cordingly, in the production of polyethylene tape of the character whichis to have its natural electrical properties undegraded by thermalabuse, the highest temperatures in the system are to be maintained aslow as possible. It has been found in operation of the process describedthat temperatures in the cylinder of approximately 360 F. and dietemperatures of 350 F. may be maintained for polyethylene tapethicknesses within the range of .070" to .085". The contour of thepassage leading from the cylinder to the exit of the die should be sodesigned as to prevent stagnation of the material as such stagnationwould cause possible degradation by exposure to heat-time factor ofdegrading character. Accordingly, the passage leading from the cylinderto the manifold 40- is of large cross section of smooth profile and themanifold 40 is of large cross section and smooth profile as comparedwith the distance between the face 45 and face 46 of the die land 42.

In the extrusion process, the take-up rolls 23 travel at such a rate asto correspond to a higher lineal velocity of the tape at this point inthe process than the lineal velocity of the tape leaving the exit of thedie IT. This difference in velocity serves to effect a pull-down ordiminishing of the. thickness of the tape so that the finished thicknessof tape will be less than the distance between the faces 45 and 46 ofthe die I! at the bottom 41." This pull-down occurs between the bottomof the die and the point where the tape enters the tempering bathwherein the tape is cooled so that the amount of pull-down or hotstretch can be controlled by varying the fluid level within thetempering bath or varying the speed of the take-up rolls 23. In theprocess described, the rollers l9 and 20 have their surfaces travelingat the same speed as the surfaces of the rollers 23. The roll I9 is solocated within the tank 28 and below the die 11 that the axial travel ofthe tape, while it is being pulled down and at least partially tempered0r cooled, is aligned with the axis of the die land 42. In the process,the amount of pull-down should be near the minimum required for propercontrol of movement of the tape through the travel recited and apull-down within the range of 25% to 30% under thev conditions hereinreferred to has been found to be satisfactory.

It will be obvious to those skilled in the art that various changes maybe made without departing from the spirit of the invention and thereforethe invention is notlimited to what is shown in the drawingsanddescribed in the specification but only as indicated-in the appendedclaims.

What is claimed is:, Y a

1. In extrusion apparatus for the production of extruded stressandstrain-free thermoplastic tape of uniform cross-sectional thicknesscomprising an extrusion cylinder and means for forcing thermoplastic tobe extruded therethrough, a die having an inlet and an outlet, a conduitform ing a passageway connecting the outlet of said cylinder with theinlet of said die, said die comprising a generally tubular manifoldhaving an inlet at one end thereof and a die land. said die land havinga length at least twenty five times the thickness of the tape to beproduced the exit velocity of the thermoplastic material along the.entire length of the die land being equalized, the axis of the die landbeing substantially at right angles to the axis of the manifold, saidmanifold extending completely across the ingress side of said die-land.I

2. The structure recited in claim 1, said die land having a length offifty times the thickness of the tape to be produced.

3. The structure recited in claim 1, said conduit being in the shape ofan elbow.

4. The structure recited in claim 1, said die comprising a plurality ofcooperating block-like elements having formed therein said manifold andsaid die land.

5. The structure recited inclaim 4, said manifold having its inletconnected to the outlet of said conduit by a hollow truncatedcone-shaped adaptor.

6. The structure recited in claim 1, said die land having asubstantially constant cross section area the entire length thereofcorresponding to the cross sectional shape of the tape to be extruded.

7. The structure recited in claim 1, said manifold having a smallercross section than said conduit.

8. The structure recited in claim 1, said manifold being of circularcross section, the cross sectional configuration of said die land beingrectangular.

9. The structure recited in claim 8, said die land having asubstantially constant cross sectional area the entire length thereof.

10. In extrusion apparatus for the production of extruded stress andstrain free thermoplastic type of uniform cross-sectional thickness, adiecomprising a generally tubular manifold having an inlet at one endthereof, and a die land, said die land having a length at least 25 timesthe thickness of the tape to be produced, the axis of the die land beingsubstantially at a right angle to the axis of the manifold, saidmanifold extending completely across the ingress side of said die land,said manifold having a relatively large diameter as compared with thethickness of the die land whereby the exit velocity of the materialbeing extruded is equalized along the entire length of the die land.

11. The structure recited in claim 10, said die comprising a pluralityof cooperating block-like elements having formed therein said manifoldand said die land.

12. In extrusion apparatus for the production of thermoplastic tape ofuniform cross-sectional thickness, a die comprising a manifold and a dieland, the axis of the die land being substantially at right angles tothe axis of the manifold, said manifold extending completely across theingress side of said die land, said die comprising a plurality ofcooperating block-like elements having formed therein said manifold andsaid die land.

13. The structure recited in claim 12, said die comprising twocooperating block-like elements wherein three faces of said die land areformed in one of said block elements and the surface of the other ofsaid block elements forms the fourth face of said die land.

14. The structure recited in claim 12, said manifold having a relativelylarge diameter as compared with the thickness of said die land wherebythe exit velocity of the material being extruded is equalized along theentire length of the die land.

LEE F. SAMLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Bailey et al Aug. 23, 1949

